CHECK: extern prototypes should be avoided in .h files
#48: FILE: tools/testing/selftests/bpf/bpf_kfuncs.h:72:
+extern struct bpf_key *bpf_lookup_user_key(__s32 serial, __u64 flags) __ksym;

WARNING: externs should be avoided in .c files
#84: FILE: tools/testing/selftests/bpf/progs/test_lookup_key.c:21:
+extern struct bpf_key *bpf_lookup_user_key(__s32 serial, __u64 flags) __ksym;

WARNING: externs should be avoided in .c files
#123: FILE: tools/testing/selftests/bpf/progs/verifier_ref_tracking.c:30:
+extern struct bpf_key *bpf_lookup_user_key(__s32 serial, __u64 flags) __ksym;

total: 0 errors, 2 warnings, 1 checks, 66 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

Commit 5aec616b1cdb ("bpf: fix key serial argument of bpf_lookup_user_key()") has style problems, please review.

NOTE: Ignored message types: ALLOC_SIZEOF_STRUCT BAD_REPORTED_BY_LINK CAMELCASE COMMIT_LOG_LONG_LINE GIT_COMMIT_ID MACRO_ARG_REUSE NO_AUTHOR_SIGN_OFF

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.
total: 0 errors, 2 warnings, 1 checks, 66 lines checked